This application claims priority to Japanese Patent Application No. 2009-262617, filed Nov. 18, 2009, the entirety of which is incorporated by reference herein.
1. Technical Field
The present invention relates to a technique for ejecting liquid through ejection nozzles.
2. Related Art
A liquid ejecting apparatus that ejects liquid such as ink from an ejection head is known in the art. A plurality of very small ejection nozzles is formed in the ejection head. Liquid (e.g., ink) that is to be ejected is contained in a dedicated container (e.g., ink cartridge). The liquid contained in the container is supplied to the ejection head through a passage. The liquid ejecting apparatus ejects the liquid supplied to the ejection head. A cap covers the ejection nozzles when they are not used for ejecting the liquid so as to prevent the moisture of the liquid from evaporating through the ejection nozzles, thereby avoiding the viscosity of the liquid from increasing.
A component having precipitating property is sometimes used as a component of liquid that is to be ejected. For example, when ink is used as the liquid that is to be ejected, pigment is sometimes used for the purpose of enhancing so-called weatherability or improving color-forming property. Pigment is not soluble in the solvent (e.g., water or alcohol) of ink and thus exists in a suspended state therein. For this reason, if ink is allowed to stand for a long period, pigment precipitates in the solvent of the ink. Because of the precipitation of the pigment, a thick part in which the concentration of the pigment is high is formed in the ink. Since the viscosity of the ink increases at the thick part, in some cases, ejection nozzles become clogged even when covered by a cap, which makes it impossible to print an image properly.
To address such a problem, the following technique has been proposed as disclosed in JP-A-2007-268997. An ink-jet printer disclosed therein uses, for printing, ink that contains a component having precipitating property (referred to as “ink having precipitating property”). Liquid that does not contain a component having precipitating property and is used for the purpose of keeping clogging-free condition has been prepared separately. When an ejection head will not be used for printing, the ink having precipitating property is discharged out of the ejection head so as to change the type of liquid in the ejection head from the ink to the clogging-free liquid. To perform printing, the clogging-free liquid is discharged out of the ejection head so as to change the type of liquid in the ejection head from the clogging-free liquid to the ink having precipitating property.
However, the above related art has a disadvantage in that, though it is possible to avoid the ejection nozzles of the ejection head from becoming clogged, after having been discharged from the ejection head, ink having precipitating property thickens or solidifies in the cap, resulting in the forming of sediment therein. The ink discharged into the cap is supposed to be drained to the outside of the cap by utilizing a force of suction applied thereto by a suction pump that is connected to the cap. However, there is a problem in that it is actually difficult to drain the ink out of the cap smoothly when the thickened or solidified ink having precipitating property blocks the inner space of the cap.